The present invention relates to sheet feeding apparatus and in particular to an adjustable sheet cassette capable of housing stacks of sheets or similar materials of different sizes.
In a particular application, the adjustable sheet cassette of the present invention has utility as a supply of stacked sheets in automatic printing apparatus such as reproducing apparatus including copiers, and electronic printers. Typically, in these devices, individual sheets of copy paper are separately fed through the copier and processed one at a time. In this process, it is convenient to have a supply stack of sheets from which to feed the individual sheets. Modern day business desires require that a copier or printer be capable of faithfully reproducing original documents of various sizes or configurations on various types of copy stock. To facilitate this operational flexibility, it has been customary to provide a supply of cut sheets in a cassette-type form. These paper sheet cassettes may be designed for a single fixed size of paper in which case they are only used for storing sheets of that size in the printing apparatus. Alternatively, adjustable cassettes may be designed to enable customer adjustment of the cassette for a variety of different sheet sizes. With the fixed size cassette if a printing operation is to be performed to obtain prints on a copy sheet size of a size other than that which is in the fixed cassette, the cassette must be removed from the machine and replaced with another cassette of a different fixed size to enable the operation to be completed. Similarly, with an adjustable cassette, if the size of the paper in the cassette is unsuitable for a particular printing operation, the copy sheets should be removed and replaced with the appropriate size copy sheets for that particular printing operation.
It is desirable that the printing apparatus know the size of the sheets in the cassette as soon as it is inserted in the printing machine. This enables the machine to automatically display the copy sheet size on the control panel to tell an operator if a particular job run can be run with the copy sheet size in the cassette or to replace the copy sheet supply. For example, it enables the operator to determine if the automatic printing machine is capable of providing size for size reproduction or automatic reduction and/or automatic enlargement of an original that may be placed on the copying platen.
For the larger, higher volume, higher speed machines, the size of a sheet in a typical, adjustable cassette, is typically determined by providing separate switches on two sides of the cassette, each with a separate input to the controller on the main body of the machine which requires wiring harnesses, plugs, etc. that must be connected after the cassette has been loaded into the automatic printing machine. Not only is this a relatively complicated procedure and expensive, but it involves an electrical connection which can easily become contaminated by dirt, toner or other debris, or otherwise damaged.
In the smaller, slower, lower volume machines, the size of the sheets in an adjustable cassette, may be entered into the control panel of the machine by the operator manually pressing a button or turning a dial, or alternatively, by the operator manually moving a sheet size indicator on the cassette, which in fact may be totally independent of the size sheet which is actually in the cassette. It frequently happens that the operator in either circumstances selects the wrong size. This permits the condition to exist where the machine interpretation of the size of the sheets in the cassette does not match the size of the sheets in the cassette and thereby leads to copy quality defects, productivity losses, in that paper jams may occur which may lead to shutting down the entire printing operation. The present invention is directed to a mechanism for automatically identifying the sheet size in an adjustable cassette without requiring any switches, wires, plugs, etc. on the cassette which have to be plugged into the machine.